Battery lifetime has become an increased strong demand from end-users of mobile computing devices such as notebook computers, netbooks and mobile Internet devices (MID). Statistics data shows that ⅔ of the users are willing to consider battery lifetime as the first or second priority, 50% of the users are willing to pay an extra battery in $30˜$40 dollars/1 hour fee. Narrow VDC (NVDC) of the power transmission structure, proposed by Intel, is one of many proposals to extend battery lifetime in mobile systems. This technology has evolved into two generations, the first generation NVDC called NVDC-I and the second-generation NVDC adaptive mobile power system (AMPS).
In Adaptive Mobile Power Systems (AMPS), the switching adapter is a key part. It is combined with the battery system of the mobile computing device to constitute a so-called Adaptive Mobile Power System (AMPS). The ideal output of the switching power adapter for Adaptive Mobile Power System (AMPS) is a constant current source characteristic. Due to its characteristics of current source, Adaptive Mobile Power System (AMPS) DC bus voltage is basically determined with the battery voltage. Due to its current source characteristics, the output of the switching adapter can directly charge rechargeable battery systems of the Adaptive Mobile Power System (AMPS). When the system load requires current, the output of the adapters can automatically assign the appropriate current to the system load, and reduce the charge current to the battery systems accordingly. In this system, when the system required load current is bigger than the output current of the switching adapter, the output of this switching adapter and the output of the battery system can be paralleled together and offer enough current for the system load.
Because Adaptive Mobile Power System (AMPS) DC bus voltage is basically determined with the battery voltage, this constant output current of the switching adapter will increase the DC bus voltage and damage the battery and all power converters hanged on the DC bus as the battery is nearly full and the system load does not need current. To avoid this issue, the adapter must have a constant current and voltage function, that means, as the DC bus voltage is over a preset voltage, the adaptor's output characteristic is converted from a constant current source into a constant voltage source with the preset voltage. This switching adapter also needs to meet Energy Star 2.0 requirements under different load conditions.
In existed switching adapters, its output is a constant voltage source. Therefore, its output can be with a relatively large output capacitor. Due to this relatively large output capacitor, with existing control scheme, the switch adapters can meet Energy Star 2.0 requirements under different load conditions. For Adaptive Mobile Power System (AMPS) application, the switching adapter must have a constant current and voltage function, that means, as the DC bus voltage is over a preset voltage, the adaptor's output characteristic is converted from a constant current source into a constant voltage source with the preset voltage, and the existed switching adapter control method is not suitable for the switching adaptor used for Adaptive Mobile Power System (AMPS).